A very complicated proceudure is required to purify polypeptides produced by microorganisms, animal cells, and plant cells, while maintaining their physiological activities to high degree. Consequently, the present procedures require some to be improvement. For example, the purification of a human growth hormone releasing factor produced by transformed microorganisms involves a ten stage procedure, resulting in a large amount of production but at a yield too low for carrying out a bioassay (Vincent Geli et al., Gene, 80, 129-136 (1989)). For the purification of human calcitonin, it has been reported that an eight stage purification is carried out, using 6 types of columns, to isolate human calcitonin (J. P. Gilligan et al., Biochromatography, 2 (1), 20-27 (1987)).
These purification steps, however, are very complicated, and thus it may be considered that they lead to the decomposition of polypeptides, and to the disappearance of physiological activities of polypeptides during the purification.
The object of the present invention is, therefore, to provide a process which can isolate polypeptides in a stable form and isolate and purify polypeptides at a high yield by carrying out a simple procedure, in order to thus solve these problems.